The invention relates to a drive screw that fastens a member to be driven so as to be first driven onto and then screwed into such member to be driven.
Generally, drive screws are often used to fasten a gypsum board to a sheet steel. A drive screw includes a large diameter portion and a small diameter portion. First, when the drive screw has been driven, the small-diameter portion goes through a sheet steel to thereby allow the large-diameter portion to stay within a gypsum board, and then the large-diameter portion is screwed into the sheet steel in the screwing phase to thereby fasten the sheet steel and the gypsum board together.
There are cases where not only a single gypsum board but also two or more gypsum boards are fastened to a sheet steel. Further, gypsum boards to be used come in large and small thicknesses. It goes without saying that a drive screw for fastening two gypsum boards or a thick gypsum board is longer than a drive screw for fastening a single gypsum board or a thin gypsum board.
By the way, there are cases where fastening involves only a single gypsum board or two gypsum boards and fastening involves a combination of a thin gypsum board and a thick gypsum board at a single construction site. In such cases, the cumbersome operation of selecting a drive screw so that the lengths of the drive screws match the thicknesses of the gypsum boards impairs operation efficiency. Therefore, a drive screw that can overcome such inconvenience has been called for.
However, the shank of a conventional drive screw for a single gypsum board is too short to fasten two gypsum boards, so that defective fastening results. On the other hand, if a drive screw for two gypsum boards is used to fasten a single gypsum board, the large-diameter portion of such drive screw passes through as far as to a sheet steel, which thus imposes the problem that a predetermined fastening force cannot be provided. Therefore, in the case of the conventional drive screw, one must change the type of drive screw depending on the thickness and number of gypsum boards.
Similar problems have been addressed not only in the case of fastening a gypsum board to a sheet steel, but also in the case of fastening a plate member such as a sheet of plywood to a piece of timber.
Furthermore, the present applicant has proposed a drillig screw adapted for screwing operation to fix a gypsum board to a light gauge channel steel whose thickness is either 0.5 mm or 0.8 mm used as structural materials for the construction of houses (Japanese Patent Application No. Hei. 7-213780). The purpose of this drilling screw is to improve screwing efficiency by allowing gypsum board screwing operation to be performed using a drive type screwing machine whose operation time is faster than an electrically-driven screwing machine involving only rotating operation.
That is, when a gypsum board is screwed using a conventional drilling screw and a drive type screwing machine, addressed are inconvenience that the preceding drilling screw that has been fastened is slacken due to impact accompanied by the driving operation of the succeeding drilling screw, that the load stress of the drilling screw is reduced to a significant degree while embedded into the gypsum board, or the like. Therefore, the conventional drilling screw has not allowed the gypsum board screwing operation to be performed using the drive type screwing machine.
A drilling screw proposed by the present applicant has overcome the aforementioned problem. That is, the drilling screw is characterized as allowing the diameter thereof to be tapered from a large-diameter parallel thread portion having a trumpet head to a small-diameter parallel thread portion via a tapered thread portion and as giving a tapered bit portion at the point of the small-diameter parallel thread portion.
When the drilling screw is driven into a gypsum board that is overlapped on a light gauge channel steel using the driver of a drive type screwing machine, the tapered bit portion and the small-diameter parallel thread portion pass through the gypsum board and the light gauge channel steel. Then, the driver starts turning the drilling screw, causing the intricately designed thread ridges of the small-diameter parallel portion to develop a thrust in a direction in which the drilling screw passes through the light gauge channel steel, so that the tapered thread portion taps the through hole in the light gauge channel steel so as to enlarge such through hole. As a result, the parallel thread portion goes through the light gauge channel steel to thereby strongly fasten the drilling screw.
As a result of the small-diameter parallel thread portion and the tapered bit portion, the aforementioned drilling screw is advantageous in the following point compared with the conventional drilling screw having such a simple shape in which a parallel thread portion and a front end tapered thread portion are formed continuously to each other. That is, the aforementioned drilling screw can reduce the deformation and vibration of the steel sheet attributable to impact accompanied by the driving of the drilling screw into a light gauge channel steel, which in turn eliminates reduction in fastening force and load stress. As a result, the screwing operation using a drive type screwing machine which has not been able to be performed with the prior drilling screws can be implemented.
However, at the time of screwing the drilling screw into a side plate portion of the light gauge channel steel, the side plate portion that is weaker in shape holding strength than the bottom portion may, in some cases, be deformed due to impact applied by the drilling screw, or the gypsum board may, in some cases, float from the channel steel. In such cases, the drilling screw is not driven deep enough into the channel steel so that the small-diameter parallel thread portion may not, in some cases, go through the steel plate. As a result, the drilling screw does not develop thrust during the turning operation, so that the drilling screw idly turns while not being screwed in.
Therefore, addressed in the aforementioned cases also are technical problems to be overcome to fasten a gypsum board and a channel steel reliably.